Manufacturing process for chalcogenide glasses

ABSTRACT

The present invention is generally directed to a method of making chalcogenide glasses including holding the melt in a vertical furnace to promote homogenization and mixing; slow cooling the melt at less than 10° C. per minute; and sequentially quenching the melt from the top down in a controlled manner. Additionally, the present invention provides for the materials produced by such method. The present invention is also directed to a process for removing oxygen and hydrogen impurities from chalcogenide glass components using dynamic distillation.

PRIORITY CLAIM

The present application is a divisional application of U.S. applicationSer. No. 13/483,023 filed on May 29, 2012 by Vinh Q. Nguyen et al.,entitled “MANUFACTURING PROCESS FOR CHALCOGENIDE GLASSES,” which was adivisional application of U.S. application Ser. No. 12/179,797 filed onJul. 25, 2008 by Vinh Q. Nguyen et al., entitled “MANUFACTURING PROCESSFOR CHALCOGENIDE GLASSES,” the entire contents of each are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally directed to a method of makingchalcogenide glasses, including rare-earth doped chalcogenide glasses,and the materials produced by such method.

2. Description of the Prior Art

To date, the typical way to melt a chalcogenide glass is to heat theelemental precursors in an evacuated and sealed quartz ampoule. Thefurnace is a rocking furnace which assists in mixing of the melt (FIG.1). After several hours of rocking at elevated temperature, the furnaceis placed at an angle of about 45 degrees and the ampoule containing themelt is pulled out, held vertical for several seconds (FIG. 2), thenimmersed in water to quench the melt. The problem is that when theampoule is set from a 45 degree angle to a 90 degree angle, the top ofthe glass melt near the meniscus undergoes turbulent viscous flow. Theglass melt surface area of the 45 degree angle (SA)₄₅ is estimated to bemore than 3 times that of the glass melt surface area of the 90 degreeangle (SA)₉₀ (FIGS. 2A and 2B). When the ampoule is quenched in water,that unstable and viscous state near the top of the glass melt is frozenin place. This leads to the typical refractive index perturbationsobserved in these glasses. In addition, the melts may interact with thequartz ampoule.

During quenching, the heat loss conduction mechanism also gives rise toa large meniscus (FIG. 3). FIG. 3A shows the meniscus of the glass meltat 400° C. just before quenching in water. FIG. 3B shows the formationof the meniscus during the quenching in water. When the ampoule issubmerged in water, the glass melt along the inner wall of the ampoulefreezes, including the bottom region of the ampoule. Heat is transferredfrom a higher temperature glass melt center region through theampoule/glass melt interface and into the water. Formation of themeniscus continues as the temperature drops due to shrinking of theglass melt via heat conduction loss mechanism through the ampoule/glassmelt interface. This conventional quenching process leads to a largemeniscus and, therefore, lower yield of useable glass. From a commercialperspective, this increases the cost of the glass.

During submersion in water, the melt quenches rapidly and leads to rapidpull away of the glass all at once from the quartz, leading to apowerful shock wave which causes cracking of the chalcogenide glass.This can be manifested as micro-cracking in the glass or can sometimeslead to catastrophic failure of the glass. This problem has preventedthe fabrication of rare-earth doped chalcogenide glass fiber lasers.

Further, metal oxides and hydrides have strong absorption bands in theinfrared wavelength region, which tend to lower the phonon energy of theglass thereby reducing radiative lifetimes of rare earth ions.Therefore, oxygen and hydrogen impurities will affect the glass quality.

The conventional method to make chalcogenide glasses, includingrare-earth doped chalcogenide glasses uses a high temperature quenchingprocess that results in a large meniscus, which yields a small volume ofuseable glass. Moreover, there are refractive index perturbations in theglass that limit the quality of the glass and fiber made from thisglass. Optical fibers made from these glasses will cost more because theglass yield is low, and refractive index perturbations will limit theiroptical performance.

BRIEF SUMMARY OF THE INVENTION

The aforementioned problems are overcome in the present invention whichprovides a process for preparing chalcogenide glasses including heatingthe glass components to a melt temperature to form a melt, holding themelt in a vertical furnace to promote homogenization and mixing, slowcooling the melt at less than 10° C. per minute, and sequentiallyquenching the melt from the top down in a controlled manner. The presentinvention also provides for the materials produced by such process. Thepresent invention is further directed to a process for removing oxygenand hydrogen impurities from chalcogenide glass components using dynamicdistillation.

In one embodiment, the chalcogenide glass is a stable glass, such asarsenic sulfide or arsenic selenide. In a further preferred embodiment,the stable glass is cooled within 50° C. of the glass transitiontemperature before quenching.

In another embodiment, the chalcogenide glass is an unstable glass, suchas a rare earth doped chalcogenide glass. In a further preferredembodiment, the rare earth doped chalcogenide glass comprises germanium,arsenic, gallium, and selenium; and the rare earth metal ispraseodymium. In an even more preferred embodiment, the rare earth dopedchalcogenide glass is cooled to within 50° C. of the glasscrystallization upon cooling temperature and below the liquidustemperature before quenching.

Another embodiment of the present invention is generally directed to aprocess for removing oxygen impurities from chalcogenide glasscomponents, including providing a two-zone furnace having a firsttemperature zone and a second temperature zone; providing a firstchamber disposed in the first temperature zone and a second chamber inthe second temperature zone, wherein the first chamber is fluidlyconnected to the second chamber such that vapors will transfer from thefirst chamber to the second chamber; providing chalcogenide glasscomponents in the first chamber in the presence of aluminum, zirconium,magnesium, or any combination thereof; and heating the first chamber toa temperature greater than the second chamber, such that purifiedchalcogenide glass components distill into the second chamber leavingany oxygen impurities in the first chamber.

Another embodiment of the present invention is generally directed to aprocess for removing hydrogen impurities from chalcogenide glasscomponents including providing a first chamber disposed in a furnace,wherein the first chamber is fluidly connected to a vacuum; providingchalcogenide glass components in the first chamber in the presence oftellurium tetrachloride; and heating the first chamber to a temperatureto vaporize an HCl species from the chalcogenide glass components andwithdrawing the HCl species from the first chamber via the vacuum. Thisembodiment may also include providing a second chamber disposed outsideof the furnace fluidly connected to the first chamber such that vaporwill transfer from the first chamber to the second chamber anddistilling the chalcogenide glass components from the first chamber tothe second chamber to form a rare-earth doped chalcogenide glass.

The chalcogenide glasses of the present invention offer many benefits inat least some embodiments of the invention. Slow cooling the glass meltsminimizes stresses during quenching. Moreover, controlled slow coolingmay enable thermal equilibrium and steady state to occur in the glassmelt. This contributes to a lower energy and stable state of the glassmelt just before quenching. This also results in a small meniscus and,therefore, higher yield. The yield of useable glass is typically greaterthan 80%, compared with typically less than 60% for the conventionalmethod. Additionally, vertical homogenization of the melt may eliminateor reduce the refractive index perturbations. The glass potentially canbe used to make high optical quality fiber at potentially reduced cost,and fibers made using the glass of the present invention may be lesssusceptible to refractive index perturbations. Therefore, cost may bereduced and fibers made from the glasses of the present invention mayhave better optical properties. Moreover, these glasses will potentiallyenable the manufacture of fiber lasers in the infrared.

The high quality glasses of the present invention may produce highoptical quality chalcogenide fibers. Chalcogenide glass transmits frombetween about 1 μm to about 12 μm, depending on composition. Theinfrared transmitting chalcogenide glasses and optical fibers encompassthe IR region of interest with numerous applications including thermalimaging, temperature monitoring, and medical applications. Also, thechalcogenide glass fibers may be developed for IR missile warningsystems and laser threat warning systems to provide superior aircraftsurvivability, and high energy IR power delivery using for example, butnot limited to, CO (5.4 μm) and CO₂ (10.6 μm) lasers. In addition, thesefibers may be developed for remote fiber optic chemical sensor systemsfor military facility clean up and other industrial applications.

The arsenic sulfide and arsenic selenide fibers described herein may bedeveloped for use in many defense applications including high energy IRlaser power delivery for infrared countermeasures and defense facilityclean up. High quality infrared transmitting optical fibers enableapplication in remote chemical sensors to detect contaminants ingroundwater, environmental pollution monitoring, other civil/industrialprocess monitoring applications as well as Raman amplifiers and alloptical ultra-fast switches for telecommunications, and fiber sources inthe infrared for sensors. In addition, IR fibers are needed forbiomedical surgery and tissue diagnostics.

Rare-earth doped chalcogenide glasses and fibers have great advantagesover rare-earth doped silica and rare-earth doped heavy-metal fluorideglass fibers because of further infrared transmission (1-10 μm) and therare-earth doped chalcogenide glasses possess lower phonon energies andconsequently, reduced multiphonon quenching. This property may enablemore efficient fluorescence in the infrared as well as emissionwavelengths that are not possible in rare-earth doped silica fibers.Rare-earth doped chalcogenide glass fibers could find widespread use asinfrared laser sources for chemical sensors systems and biomedicalsurgery/cauterization, as well as improved optical amplifiers fortelecommunications.

These and other features and advantages of the invention, as well as theinvention itself, will become better understood by reference to thefollowing detailed description, appended claims, and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of an example of a quartz ampoulecontaining arsenic sulfide (As—S) glass melt inside a rocking furnacewith a 45 degree inclination angle.

FIG. 2 is schematic drawing of an example of a quartz ampoule containingarsenic sulfide glass melt set at a 90 degree angle from the 45 degreeangle before quenching. The top volume of the glass melt near themeniscus undergoes turbulent viscous flow due to the shift from asurface area when the ampoule is at a 45 degree angle (A) to a reducedsurface area when the ampoule is set at a 90 degree angle (B).

FIG. 3 is a schematic diagram showing (A) a glass melt meniscus at 400°C. before quenching in room temperature water and (B) the formation ofmeniscus via heat conduction loss at glass melt/ampoule interface andshrinkage of glass melt in accordance with a conventional quenchingprocess.

FIG. 4 is a schematic diagram of an example of a quartz ampoulecontaining a glass melt inside a furnace with a 90 degree inclinationangle (i.e. vertical), in accordance with the present invention.

FIG. 5 is a nucleation and crystal growth rate curve for chalcogenideglasses.

FIG. 6 is a schematic representation of an oxide removal processincluding (A) forming of oxide with the presence of aluminum at hightemperature and (B) removing oxide through distillation.

FIG. 7 is a schematic representation of a hydrogen impurities removalprocess using dynamic distillation including (A) removal of the HCl gasspecies and (B) Ge—As—Se glass distillation with Pr doping.

FIG. 8 is a schematic diagram of the meniscus of the arsenic sulfideglass melt at (A) 500° C. and (B) 220° C.

FIG. 9 is a schematic drawing of an air quenching process of oneembodiment of the present invention.

FIG. 10 is a schematic diagram of the meniscus of the rare earthPr-doped (Ge—As—Ga—Se) glass melt at (A) 750° C. and (B) 650° C.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally relates to a new process to increase theuseable yield of stable and unstable chalcogenide glasses, includingrare-earth doped chalcogenide glasses. The present invention includes achalcogenide glass product having a reduced meniscus, which may reduceor eliminate refractive index perturbations. The present invention alsoincludes procedures for removing oxygen and hydrogen impurities fromchalcogenide glasses.

In one embodiment of the present invention, the components for achalcogenide glass are heated to form a melt inside a quartz ampoule.The heating takes place inside a rocking furnace to facilitate mixing ofthe melt. The melt can stay in the rocking furnace for several hours.Then, the ampoule is pulled out of the rocking furnace at elevatedtemperatures while the melt is still fluid. As shown in FIG. 4, the meltis then held vertical and placed in a vertical furnace for up to severalhours to allow mixing and homogenization of the top surface (turbulentmaterial) on going from a 45 degree angle to the vertical position.

Next, the melt is slow cooled. To slow cool the melt, the temperature isreduced by less than 10° C. per minute, and more preferably by less than5° C. per minute. Controlled slow cooling enables thermal equilibriumand steady state to occur in the glass melt at all time. Thiscontributes to a lower energy and stable state of the glass melt justbefore quenching. This also results in a small meniscus and thereforehigher yield in useable glass. Vertical homogenization of the meltreduces or eliminates the refractive index perturbations. Fibers madeusing glass prepared in this manner should have reduced refractive indexperturbations.

Determining how much to cool the melt depends on whether the glass isstable or unstable and on the applicable Nucleation and Crystal GrowthRate Curve (e.g., FIG. 5). Crystallization in the melt should be avoidedbecause it leads to a poor quality glass which will scatter light morestrongly. Further, the crystallization of rare-earth doped chalcogenideglasses leads to rare-earth ion clustering which impedes the rare-earthion emission.

As shown in FIG. 5, there is no nuclei or crystal growth at the glasstransition temperature (T_(G)). Upon heating, small nuclei begin to format the nucleation onset temperature (T_(N)). At the crystallizationonset upon heating temperature (T_(XH)), crystals begin to grow on thesenuclei. Above the liquidus temperature on heating (T_(L)), all thecrystals melt to form a liquid. Upon cooling below T_(L), no crystalscan form until the temperature is at or below the crystallization onsetupon cooling temperature (T_(XC)). Below T_(XC), the nuclei form andcrystals grow, especially between T_(XC) and T_(XH).

Stable chalcogenide glasses, such as arsenic selenide and arsenicsulfide, do not crystallize easily when quenched slowly from elevatedtemperatures to their glass transition temperatures. Therefore, thesestable glasses are slowly cooled to within 50° C. above T_(G) (i.e.,between T_(G) and T_(G)+50° C.) before quenching since nuclei andcrystal growth are absent. More typically, they are cooled to within 30°C. above T_(G).

For unstable chalcogenide glasses, including rare-earth dopedchalcogenide glasses, the glass melt should be cooled to within 50°above T_(XC) (i.e., between T_(XC) and T_(XC)+50° C.) but below T_(L)before quenching to prevent crystal formation. The various temperatures(e.g. T_(G), T_(XH), T_(XC), and T_(L)) will vary somewhat from oneglass system to another. Table 1 shows an example of the varioustemperatures for two unstable glasses (a rare-earth doped core and anundoped clad). Both glasses were cooled to 650° C. before quenching,which was 25° C. above T_(XC) and below T_(L).

TABLE 1 Various temperatures for two unstable chalcogenide glasses.Glass T_(quench) (° C.) T_(G) (° C.) T_(XH) (° C.) T_(XC) (° C.) T_(L)(° C.) RE doped core 650 265 575 625 725 Clad 650 265 575 625 725

Once cooled to the temperature described above, the glass is quenched ina controlled manner to cool from the top surface down. This enables theglass to quench sequentially and prevents a shock wave from forming.Also, lowering the temperature before quenching minimizes stressesduring quenching. The glass can be quenched using air flow (or other gase.g. Ar, N₂, etc) or using liquid, e.g., water.

The present invention also includes a method of removing oxygen andhydrogen impurities from doped and undoped chalcogenide glasses. Oxygenand hydrogen impurities in the glass should be removed since the metaloxides have strong absorption bands in the infrared wavelength region,which tend to lower the phonon energy of the glass thereby reducingradiative lifetimes of the rare earth ions. Oxygen removal isaccomplished using two connected chambers in a two-zone (ortwo-temperature) furnace (FIG. 6) to facilitate distillation of glassprecursors in the presence of addition of aluminum. The glass distillsfrom chamber A in the first zone to chamber B in the second zone leavingoxide impurities in chamber A. In a subsequent distillation process,hydrogen impurities can be removed by dynamic distillation in thepresence of tellurium tetrachloride (TeCl₄). (See, e.g., FIG. 7.) Inparticular, the presence of TeCl₄ in the glass melt enables theformation of hydrogen chloride (HCl) at 700° C., which is dynamicallyremoved from the chamber. Using a two zone furnace, this seconddistillation process can also be used to dope the glass with therare-earth elements, for example, praseodymium (Pr) as shown in FIG. 7.

This invention can also be applied to other chalcogenide glass systemssuch as multicomponent As—S containing glasses as well as As—Secontaining glasses such as arsenic selenide (As—Se) and telluride basedglasses (Ge—As—Se—Te). In addition, this invention can be used to quenchany chalcogenide glass melt doped with rare earth elements or even othermelts which tend to typically crystallize on regular cooling.

EXAMPLE 1 Example of Material Involving Stable Chalcogenide Glasses

First, 47.92 grams of arsenic and 32.08 grams of sulfur precursors (atotal of 80 grams) were batched in a silica ampoule with a compositionof As₃₉S₆₁. The ampoule was evacuated for 4 hours at 1×10⁻⁵ Torr. Theampoule was sealed using a methane/oxygen torch. Inside a rockingfurnace with a 45 degree angle inclination, the ampoule containing thearsenic and sulfur precursors was melted at 450° C. for 4 hours. Forhomogenization mixing and uniform glass melting, the temperature wasincreased to 600° C. for 4 hours and 800° C. for 10 hours. Next, therocking furnace was set at a 45 degree inclination and the temperaturewas lowered to 700° C. for 1 hour. The ampoule was transferred from the45 degree furnace into another vertically 90° furnace with thetemperature set at 700° C. (FIG. 4). The temperature of the verticalfurnace was set at 700° C. for 1 hour for homogenization and uniformmixing. Next, the temperature of the vertical furnace was decreasedslowly from 700° C. to 500° C. at 1° C./min, and held at 500° C. for 1hour. Then the temperature of the vertical furnace was decreased from500° C. to 220° C. at 1° C./min and held at 220° C. for 30 minutes,which is 20° C. above T_(G). This controlled slow cooling lowered theenergy state of the arsenic sulfide glass melt and enabled the formationof stable As—S glass resulting in a very small meniscus as seen in FIG.8.

Next, the ampoule was raised above the vertical furnace and air quenchedusing the copper circular ring assembly (FIG. 9) in a controlled manneras described below. The ampoule is pulled through the copper circularring assembly to provide symmetrical cooling conditions on all sides ofthe ampoule. The top of the glass melt near the meniscus was quenchedfirst. In this embodiment, 60 psi of room temperature air was circulatedthrough the copper circular ring assembly. The pressure could be higheror lower depending on the configuration of the system as well as themass and volume of the glass. When the top of the glass melt hadquenched and pulled away from the ampoule, the ampoule was slowly raisedand subsequent portions of the ampoule were air quenched sequentiallyuntil all sections of the glass rod completely quenched and pulled awayfrom the ampoule. The arsenic-sulfide ampoule was then put inside anannealer with a set point at 180° C. and was annealed at 180° C. for 6hours and slowly cooled from 180° C. to room temperature at 1° C./min.

FIGS. 8A and 8B show the schematic diagram of the controlled slow coolfor the arsenic sulfide glass melt at 500° C. and 220° C., respectively.Since the glass melt was being cooled very slowly, the temperature atany point inside the glass melt always reached equilibrium state, i.e.,there is no temperature gradient between the center of the glass meltand the outer region next to the ampoule inside wall. This results insmall meniscus as shown in FIG. 8B.

Photographs of the one inch arsenic sulfide glass rods quenched usingthe process of the present invention and the conventional rapid quenchprocess show that the meniscus length in a comparative example glass rodobtained from a conventional process is about 10 times larger than thatof a glass rod using the slow cool process of the present invention. Infact, the useable glass is now greater than 80% of the total volumecompared with only about 60% using conventional quenching methods.

In a similar manner, 70.656 grams of arsenic and 49.344 grams of sulfurwere used to make a 120 grams 1-in diameter glass cullet of cladcomposition As₃₈S₆₂ suitable for the As₃₉S₆₁ core composition.

The arsenic sulfide glass cullets with a nominal core (As₃₉S₆₁) and clad(As₃₈S₆₂) compositions were drawn into optical fiber using a controlleddouble crucible process. The fibers were drawn under inert atmosphere ata rate of approximately 5.0 meters per minute. The fibers were free fromreactive index perturbations when examined using optical microscopy.

EXAMPLE 2 Example of Material Involving Rare-Earth Doped ChalcogenideGlasses

Oxide impurities present in the starting components (germanium, arsenic,and selenium) were removed by melting the precursors with the additionof 10 ppm of aluminum, zirconium, magnesium, or any combination thereof.First, 14.905 grams of germanium, 13.631 grams of arsenic, 51.102 gramsof selenium, and 0.008 grams of aluminum precursors (approximately79.646 grams) were batched in a silica ampoule in chamber A (FIG. 6).Table 2 shows the typical batch size to make about 80 grams of corecullet. The ampoule was evacuated for 4 hours at 1×10⁻⁵ Torr. Theampoule was sealed using a methane/oxygen torch.

TABLE 2 Batch calculations for making ~80 grams of core culletrare-earth doped glass rod with Ge_(19.75)AS_(17.5)Ga_(0.5)Se_(62.25)composition 80 g Mol % Mol. Wt. batch Ge 19.750 72.59 14.905 As 17.50074.922 13.631 Ga 0.500 69.72  0.362 Se 62.250 78.96 51.102 100.000~80.000  

The ampoule (chamber A) was placed in the first zone of a two-zonefurnace for the glass melting, homogenization, and distillationprocesses. Within the furnace, chamber A is fluidly connected to chamberB, which is placed in the second zone of the two-zone furnace, asillustrated in FIG. 6. The two-zone furnace is set at a 45 degree angle.The glass melting schedules are given in Step-1 in Table 3. When all theglass melt was distilled over into chamber B during Soak Time 3 inStep-1 from Table 3, chamber B is pulled out of the furnace and quenchedin water. Oxide impurities remain in chamber A.

TABLE 3 Glass melting schedules used in making 80 grams of core culletrare- earth doped glass rod with Ge_(19.75)AS_(17.5)Ga_(0.5)Se_(62.25)composition Step - 2 Step - 3 Step - 4 Step - 1 Zone 1 Zone 1 Zone 1Zone 1 Zone 2 & 2 & 2 & 2 Ramp 1 (° C./min) 5 5 5 5 5 Soak Temp 1 (° C.)500 550 850 280 500 Soak Time 1 (hrs.) 1 1 12 4 1 Ramp 2 (° C./min) 5 510 2 5 Soak Temp 2 (° C.) 850 900 700 400 850 Soak Time 2 (hrs.) 12 12 34 2 Ramp 3 (° C./min) 5 5 2 5 Soak Temp 3 (° C.) 900 400 500 950 SoakTime 3 (hrs.) 12 4-12 4 1 Ramp 4 (° C./min) 2 5 Soak Temp 4 (° C.) 625850 Soak Time 4 (hrs.) 4-12 15 Ramp 5 (° C./min) 5 Soak Temp 5 (° C.)750 Soak Time 5 3

After the ampoule was quenched from Step-1 of Table 3, chamber B wasbroken near the top and 0.014 g of TeCl₄ added. The ampoule containingthe distilled glass and TeCl₄ was evacuated for 4 hours at 1×10⁻⁵ Torr.The ampoule was sealed using a methane/oxygen torch. The ampoule wasplaced in a two-zone rocking furnace (FIG. 1) and was melted andhomogenized using the schedule in Step-2 of Table 3. This melting wasperformed with the furnace rocking to mix and homogenize the glass. Theglass at the end of Soak Time 2 in Step-2 was quenched at 700° C. inwater and saved as a core cullet. The presence of TeCl₄ in the glassmelt enabled the formation of HCl species at 700° C. The tellurium issoluble in the glass.

From Step-2, 14.918 grams of the core cullet was loaded into anotherampoule, i.e., chamber A in FIG. 7. In order that the glass israre-earth doped, approximately, 0.068 grams of gallium and 0.014 gramsof praseodymium were loaded into chamber B of the ampoule as shown inFIG. 7. The composite is described in Table 4. Chamber A of the ampoulewas placed inside the two-zone furnace while chamber B was placedoutside the furnace and hooked to a vacuum system. The furnace wasturned on with the heating schedule of Step-3 in Table 3. As discussedabove, the presence of TeCl₄ in the glass melt enabled the formation ofHCl species. From Step-3 in Table 3, as the furnace was heated up fromSoak Temperature 1 of 280° C. to Soak Temperature 4 of 625° C. the HClgas species was dynamically removed by the vacuum before thedistillation of the glass melt took place (FIG. 7A). At Soak Temperature4 of 625° C. in Step-3, the glass melt was dynamically distilled fromchamber A into chamber B. The furnace was turned off and chamber A ofthe ampoule was removed by sealing off using a methane/oxygen torch atsection C. Next, chamber B was sealed at section D.

TABLE 4 Batch calculations for making 15 grams of core cullet rare-earthdoped glass rod with Ge_(19.75)AS_(17.5)Ga_(0.5)Se_(62.25) composition15 g Batch Cullet 14.918 Ga 0.068 Pr 0.014 15.000

The ampoule containing the oxygen- and hydrogen-free glass cullet,gallium, and praseodymium was put inside a two-zone rocking furnace(FIG. 1). The glass melting and homogenization furnace schedule is shownin Step-4 of Table 3. At the end of the melting cycle Soak Time 5 of750° C., the rocking furnace was stopped and the glass ampoule wastransferred into the vertical 90 degree furnace preheated to 750° C.(FIG. 9). Table 5 shows the glass melting schedules used in making 15grams of core cullet rare-earth Pr doped glass rod withGe_(19.75)As_(17.5)Ga_(0.5)Se_(62.25) composition in the verticalfurnace.

TABLE 5 Glass melting schedules in the vertical furnace used in making15 grams of core cullet rare-earth Pr doped glass rod withGe_(19.75)AS_(17.5)Ga_(0.5)Se_(62.25) composition. Step - 5 Ramp 1 (°C./min) 5 Soak Temp 1 (° C.) 750 Soak Time 1 (hrs.) 3 Ramp 2 (° C./min)5 Soak Temp 2 (° C.) 850 Soak Time 2 (hrs.) 1 Ramp 3 (° C./min) 3 SoakTemp 3 (° C.) 650 Soak Time 3 (hrs.) 2

The temperature of the vertical furnace was set at 850° C. for 1 hourfor homogenization and uniform mixing (Step-5 in Table 5). Next, thetemperature of the vertical furnace was decreased slowly from 850° C. to650° C. at 3° C./min, and held at 650° C. for 2 hour for equilibrium tooccur. The liquidus temperature of this glass is estimated to be about725° C. Therefore, it was at least 50° C. below the liquidus temperatureand at least 50° C. above T_(XC) before quenching. Next, the ampoule wasraised above the vertical furnace and air quenched using the coppercircular ring assembly (FIG. 6). The top of the glass melt near themeniscus was quenched first using 60 psi of room temperature air. Whenthe top of the glass melt has quenched and pulled away from the ampoule,the ampoule was slowly raised and air quenched sequentially until allsections of the glass rod completely quenched away from the ampoule. Therare-earth Pr doped Ge—As—Ga—Se glass ampoule was then put inside anannealer with a set point at 300° C. and was annealed at 300° C. for 4hours and slowly cooled from 300° C. to room temperature at 1° C./min.

FIGS. 10(A) and (B) show the schematic diagram of the meniscus of therare-earth Pr doped Ge—As—Ga—Se glass melt at 750° C. and 650° C.,respectively. Since the glass melt was being cooled slowly to 650° C.,the temperature at any point inside the glass melt always reachedequilibrium state, i.e., there was no temperature gradient between thecenter of the glass melt and the outer region next to the ampoule insidewall. In addition, the glass melt at 650° C. has a lower energy statethan that at 750° C. This process results in no refractive indexperturbations in the glass and a smaller meniscus is observed as shownin FIG. 10B. Notice that the meniscus length in the glass rod obtainedfrom a conventional process (FIG. 10A) is about 4 times larger than thatof the glass rod using the process of the present invention (FIG. 10B).In fact, the useable glass is now greater than 80% of the total volumecompared with only about 60% using conventional techniques.

EXAMPLE 3 Example of Material Involving Unstable Undoped ChalcogenideGlasses

Optical fiber cladding material for unstable rare-earth dopedchalcogenide glasses are often made using unstable undoped chalcogenideglasses. The unstable glasses require a similar technique forpurification and cooling. The oxide removal process is similar to theoxide removal step used for making the rare-earth doped core materialdiscussed in Example 2 above. The oxide impurities present in thestarting components (germanium, arsenic and selenium) are removed bymelting the precursors with the addition of 10 ppm of aluminum. First,14.935 grams of germanium, 14.230 grams of arsenic, 49.989 grams ofselenium, and 0.008 grams of aluminum precursors (approximately 79.162grams) were batched in a silica ampoule. Table 6 shows the typical batchsize to make a 79.162 gram clad cullet. The ampoule was evacuated for 4hours at 1×10⁻⁵ Torr. The ampoule was sealed using a methane/oxygentorch.

TABLE 6 Batch calculations for making ~80 grams of clad cullet withGe_(19.5)As₁₈S_(2.5)Se₆₀ composition 80 g Mol % Mol. Wt. batch Ge 19.5072.59 14.936 As 18.00 74.922 14.230 Se 60.00 78.96 49.989 S 2.50 32.064 0.846 100.00 ~80.000  

The ampoule was placed in a two-zone furnace (FIG. 6) for the glassmelting, homogenization, and distillation processes. The glass meltingschedules are given in Step-1 in Table 7. When all the glass melt wasdistilled from chamber A to chamber B over during Soak Time 3 in Step-1from Table 7 (FIG. 9), chamber B was pulled out of the furnace andquenched in water.

TABLE 7 Glass melting schedules for making 80 g of clad cullet withGe_(19.5)As₁₈S_(2.5)Se₆₀ comp. Step - 1 Step - 2 Zone 1 Zone 2 Zone 1 &2 Ramp 1 (° C./min) 5 5 5 Soak Temp 1 (° C.) 500 550 850 Soak Time 1(hrs.) 1 1 15 Ramp 2 (° C./min) 5 5 10 Soak Temp 2 (° C.) 850 900 650Soak Time 2 (hrs.) 12 12 3 Ramp 3 (° C./min) 5 5 Soak Temp 3 (° C.) 900400 Soak Time 3 (hrs.) 12 4-12 Ramp 4 (° C./min) Soak Temp 4 (° C.) SoakTime 4 (hrs.) Ramp 5 (° C./min) Soak Temp 5 (° C.) Soak Time 5

After chamber B was quenched, the ampoule was broken near the top and0.0846 g of sulfur (S) was added to give a composition ofGe_(19.5)As₁₈S_(2.5)Se₆₀ to lower the refractive index of thechalcogenide glass. The ampoule containing the distilled glass and S wasevacuated for 4 hours at 1×10⁻⁵ Torr. The ampoule was sealed using amethane/oxygen torch. The ampoule was placed in a two-zone rockingfurnace (FIG. 1) and was melted and homogenized using the schedule inStep-2 of Table 7. This melting was performed with the furnace rockingto mix and homogenize the glass. At the end of the melting cycle SoakTime 5 of 650° C., the rocking furnace was stopped and the glass ampoulewas transferred into the vertical 90 degree furnace preheated to 750° C.Table 8 shows the glass melting schedules for the clad rod withGe_(19.5)As₁₈S_(2.5)Se₆₀ composition.

TABLE 8 Glass melting schedules for the clad rod withGe_(19.5)As₁₈S_(2.5)Se₆₀ composition. Step - 6 Ramp 1 (° C./min) 5 SoakTemp 1 (° C.) 750 Soak Time 1 (hrs.) 3 Ramp 2 (° C./min) 5 Soak Temp 2(° C.) 850 Soak Time 2 (hrs.) 1 Ramp 3 (° C./min) 5 Soak Temp 3 (° C.)700 Soak Time 3 (hrs.) 1 Ramp 4 (° C./min) 2 Soak Temp 4 (° C.) 650 SoakTime 4 (hrs.) 1

The temperature of the vertical furnace was set at 850° C. for 1 hourfor homogenization and uniform mixing. Next, the temperature of thevertical furnace was decreased slowly from 850° C. to 700° C. at 5°C./min, and held at 700° C. for 1 hour for equilibrium to occur. Thenthe temperature was decreased slowly from 700° C. to 650° C. at 2°C./min and held at 650° C. for 1 hour for equilibrium to occur. Thequench temperature (650° C.) is higher than T_(XC) to preventcrystallization of the glass melt before crystallization of the unstableglass can occur.

Next, the ampoule was raised above the vertical furnace and air quenchedusing the copper circular ring assembly (FIG. 9). First, the top of theglass melt near the meniscus was quenched using 60 psi of roomtemperature air. When the top of the glass melt has quenched and pulledaway from the ampoule, the ampoule was slowly raised and air quenchedsequentially until all sections of the glass rod completely quenchedaway from the ampoule. The Ge—As—S—Se glass ampoule was then put insidean annealer with a set point at 300° C. and was annealed at 300° C. for4 hours and slowly cooled from 300° C. to room temperature at 1° C./min.Similar to that of the core rod (FIG. 10), the clad rod obtained usingthe new process also has no refractive index perturbations and aconsiderably smaller meniscus compared to the conventional waterquenched process.

The glasses of Examples 2 and 3 were drawn into optical fiber using acontrolled double crucible process. The fibers were drawn under inertatmosphere at a rate of approximately 5.0 meters per minute. The fiberswere free from refractive index perturbations when examined usingoptical microscopy. Single mode fibers should exhibit excellentqualities for making infrared fiber lasers.

The above descriptions are those of the preferred embodiments of theinvention. Various modifications and variations are possible in light ofthe above teachings without departing from the spirit and broaderaspects of the invention. It is therefore to be understood that theclaimed invention may be practiced otherwise than as specificallydescribed. Any references to claim elements in the singular, forexample, using the articles “a,” “an,” “the,” or “said,” is not to beconstrued as limiting the element to the singular.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. A rare-earth doped chalcogenide glass make by aprocess comprising the steps of: providing a first chamber disposed in afurnace; providing all chalcogenide glass components in the firstchamber in the presence of tellurium tetrachloride; providing a secondchamber disposed outside of the furnace fluidly connected to the firstchamber such that vapors will transfer from the first chamber to thesecond chamber, wherein the second chamber is fluidly connected to avacuum; providing rare-earth elements in the second chamber wherein therare-earth elements are in the second chamber when the chalcogenideglass components are in the first chamber; heating the first chamber toa temperature to vaporize an HCl species from the chalcogenide glasscomponents and withdrawing the HCl species from the first chamber viathe vacuum; after withdrawing the HCl species, distilling thechalcogenide glass components from the first chamber to the secondchamber; and heating and rocking the second chamber to form a rare-earthdoped chalcogenide glass.
 2. The rare-earth doped chalcogenide glass ofclaim 1, wherein the chalcogenide glass is a stable glass.
 3. Thechalcogenide glass claim 1, wherein the chalcogenide glass comprisesarsenic sulfide or arsenic selenide.
 4. The chalcogenide glass of claim1, wherein the chalcogenide glass is an unstable glass.
 5. Thechalcogenide glass of claim 1, wherein the rare earth metal ispraseodymium.
 6. The chalcogenide glass of claim 1 wherein thechalcogenide glass comprises germanium, arsenic, gallium, and selenium.